1. Field of the Invention
This invention relates to apparatus for feeding sheets to a sheet fed printing press and more particularly to apparatus for feeding sheets to a sheet fed printing press including means to adjust the buckling of the sheet.
2. Description of the Prior Art
It is known to provide pairs of feed rolls mounted adjacent the delivery end of a feedboard and adjacent to a transfer cylinder. It is further known, as illustrated in U.S. Pat. No. 2,708,405, to drive the feed rolls in timed relation with the transfer cylinder and the other portions of the printing press. The sheets are fed along an inclined feedboard and move into butting relation with front stops or guides to preregister the front or leading edge of the sheet. The sheets are thereafter moved transversely against side guides to register the side edge of the sheets on the feedboard. After the front and side register of the sheet, the sheet is engaged by the driven feed rolls and conveyed at a velocity higher than the circumferential or peripheral velocity of the transfer cylinder into butting relation with a register bar on a rotating cylinder. The higher speed causes the individual sheets to buckle adjacent their front edge as the sheet abuts the front register bar to assure proper register of the sheet prior to the sheet being engaged by the grippers on the transfer cylinder.
As is illustrated in U.S. Pat. No. 2,706,405, the apparatus with which the driven feed rolls are oscillated includes gear segments and a plurality of gear wheels. A high degree of accuracy or precision is required in the forming of the gear segments and the gear wheels to minimize loss of register due to the clearance between the gear teeth. Also because the motion imparted to the feed rolls by the plurality of gears and gear segments is an oscillatory motion, the inertia of the gears during reversal results in gear backlash and loss of precise register. There is a need for a feeder apparatus that eliminates the inaccuracies caused in sheet register by the gears and gear segments that drive the feed rolls.
It is also known to adjust the amount of buckling of the front portion of the sheet. Adjustment in sheet buckling must be made when sheets of different thicknesses, as for example relatively thin or tissue type sheets and relatively thick or paperboard sheets, are fed into the press. The degree of buckling should be at a minimum with relatively thick sheets and, to assure proper register, should be increased with the relatively thin sheets. Mechanical adjusting devices are known to control the amount of buckling of the sheets. Adjustment by the known adjusting devices can only be accomplished when the press is stopped. There is a need for an adjusting apparatus that permits adjusting the degree of sheet buckling while the press is in operation to provide a more precise front register on the rotating cylinder.